1. Field of the Invention
This invention relates to a method for making separate connections between a plurality of circuit contacts, including at least one contact which is to be excluded from a completed circuit.
2. The Prior Art
If several similar parts of a circuit are made together as a unit and if they are then tested, the entire circuit arrangement will be useless if the test shows that one part of the circuit does not work. This problem appears in integrated solid state memories, the manufacture of which requires hundreds or thousands of identical storage cells with a corresponding amount of components, such as transistors, diodes, and resistors all produced simultaneously in a semiconductor substrate. The problem can be solved, or at least reduced, if one or several surplus parts of a circuit are made, so that the final connecting of the circuit arrangement, i.e. the providing of separate connections between the contacts belonging to the parts of the circuit, electric supply lines, etc., takes place after the parts of the circuits have been tested. In this manner defective parts of the circuit can be excluded and only intact parts included in the circuit arrangement.
Prior art processes are known which follow this principle. U.S. Pat. No. 3,553,830, for instance, describes a process where undesired line connections are destroyed by short pulses of high electric currents. However, this process can only be applied when much space is available for specific large area current supplies which practically always is undesirable. In U.S. Pat. No. 3,771,217 a process is described where, on the basis of test results and a computer program, a unique pattern is established by means of a controlled light beam used to expose a negative photoresist which covers a layer of conductive line material on the circuit arrangement. After the development of the photoresist layer, which leaves the exposed areas in place, the non-masked conductive line material is etched off, and there remains a conductive line pattern which is connected to functioning parts of the circuit only. This process is highly time-consuming and involves expensive apparatus because an entire mask must be generated for each complete circuit combination.